Problem when process gold filled scrap with HNO3

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N

no mercy

Member
Joined
Aug 22, 2011
Messages
8
Hello everyone,

Im trying to process some gold filled scrap with HNO3, but there is a problem. Some metal dissolved in HNO3 but there is 1 metal remain, it is in silver color (not aluminum, its heavier).
Then I cleaned the remain gold filled scrap, pour some HCl to them but still no reaction. I take a picture of what remained, please help me :cry:
 

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You will not enjoy success without heating your dilute nitric.

Be advised, that material (what ever it is) responds in a rather interesting way. DO NOT USE A LOT OF ACID. Keep the vessel filled no more than 10%, and heat it to boiling. At a critical temperature, it will start dissolving, and foam like crazy. It may overflow, so keep an eye on it, and be prepared to introduce water to slow the reaction. It will be slow to dissolve, but persistent heating will do the job. I used to run them by the hundreds, if not the thousands. They are the only material I ever processed that caused boil-overs, in spite of my best attempts.

If you have much to run, you are well advised to filter everything, then incinerate the solids (after the nitric digest), then follow up with a wash in HCl, before dissolving the values.

Harold
 
Most GF glass frames are a real pain in my opinion. They are most likely some grade of nitric resistant steel so nitric won't help and HCL will be painfully slow to work. I'm talkin all day if not more to digest. I can think of a couple of options but they won't be popular.
 
Actually, the opposite will occur. The steel would dissolve and not the gold. The gold will only go into solution when there is little to no base metal left. AR is one of the unpopular options that I was talking about. But sometimes AR really is the only way to remove base metals. The other is silver.

I'll sometimes use this technique when there is a great amount of steel. Watchband caps come to mind. Nitric will only take you so far with caps. So when the nitric no longer attacks the caps, and I don’t feel like using AR for one reason or another, I'll use silver. I use sterling to kill two birds with one stone as I would have to dissolve the silver for refining anyway. I simply put the silver in with the now passivated steel and dissolve. As the silver dissolves the steel will continuously plate out the silver. This of course will put the steel into solution. When the reaction is vigorous this is all automated but when the amount of stainless is substantially reduced you will need to agitate the reaction. This reaction is done until all the steel AND silver is in solution. If you're really patient you can get it to the point where all that's left is your silver solution and gold foils. If there are especially stubborn pieces that will take forever to go into solution then you can decant the silver solution and go to the AR phase. There should be very little steel left and the gold should go into solution easily. I used to hate when there were silver watchband caps in my lots but this is how I discovered I could do this. Ok let's pick this apart now.
 
wouldnt that take some time and patience to master? it seems like a kind of touch and go process. if you go long, you can precipitate iron from a saturated solution and if you cut it short, you will have undissolved steel mixed with your gold. im not critiquing your method as ive never done it. im just saying, from your description, theres a lot of room for error for someone like me.
 
Thank you goldenchild,

From the very first time I do put some silver into when boiling these gold filled scraps in HNO3, but those "pain in the butt" steels are still there. I think I should go with AR :mrgreen:

Edited by Harold.
Please clean up your language.
 
as long as theres no tin solder involved, it should be ok. did you give the material a hot hcl bath? this will remove any highly reactive base metal (aluminum,zinc,tin)
 
Yes I do boiling them in HNO3, then clean them, pour in some HCl (no reaction). I think all metals except gold & this "pain in the butt" steel are remain :mrgreen:
 
no mercy said:
Yes I do boiling them in HNO3, then clean them, pour in some HCl (no reaction). I think all metals except gold & this "pain in the butt" steel are remain :mrgreen:
Click to expand...

ok. maybe you should try boiling them in hcl FIRST and then incinerate. then when you go to nitric acid, you will have fewer problems. hcl will digest iron much better and faster than nitric acid. if you let the frames stay in the hcl bath at a rolling boil long enough, it could remove all the iron. the trick is to get the material and the solution hot enough for the iron to become reactive. you will see the tiny bubbles emitted during the reaction.
 
Geo said:
wouldnt that take some time and patience to master? it seems like a kind of touch and go process. if you go long, you can precipitate iron from a saturated solution and if you cut it short, you will have undissolved steel mixed with your gold. im not critiquing your method as ive never done it. im just saying, from your description, theres a lot of room for error for someone like me.
Click to expand...

Everything takes time and patience in this field :p Silver should be the only thing precipitating using this method. Saturation won't be an issue because you would be adding fresh nitric and water to the reaction as necessary. If the quantity of solution becomes too great or you suspect the solution is saturated somehow, you simply remove and add fresh solution.
 

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